1. Field of the Invention
Embodiments of the invention relate to algorithms for the processing of acquired image data and the reconstruction of images from data collected using an imaging modality and, more particularly, to imaging modalities such as a PET or SPECT imaging modality, a computed tomography (CT) or magnetic resonance imaging (MRI) imaging modality, and a combined imaging modality, such as a PET/CT or SPECT/CT imaging system.
2. Description of Related Art
In positron emission tomography (PET) imaging and single positron emission computed tomography (SPECT) imaging, a radiopharmaceutical is administered to a patient. The radiopharmaceutical is typically selected so as to be preferentially or differentially distributed in the body based on the physiological or biochemical processes in the body. For example, a radiopharmaceutical may be selected that is preferentially processed or taken up by tumor tissue. In such an example, the radiopharmaceutical will typically be disposed in greater concentrations around tumor tissue within the patient.
In the context of PET imaging, the radiopharmaceutical typically breaks down or decays within the patient, releasing a pair of gamma rays moving in opposite directions in the process. In SPECT imaging, a single gamma ray is generated when the radiopharmaceutical breaks down or decays within the patient. These gamma rays interact with detection mechanisms within the respective PET or SPECT scanner, which allow the decay events to be localized, thereby providing a view of where the radiopharmaceutical is distributed throughout the patient. In this manner, a caregiver can visualize where in the patient the radiopharmaceutical is disproportionately distributed and may thereby identify where physiological structures and/or biochemical processes of diagnostic significance are located within the patient.
The PET or SPECT examination may be conducted over a relatively lengthy time interval, such as over the course of twenty-five to thirty minutes. That is, the decay process associated with the radiopharmaceutical may take place over a period of time, during which measurements are collected and during which the patient must remain relatively still. However, it may be difficult for a patient to remain perfectly still over the period of time involved in such an examination. Further, even discounting the voluntary or controllable motions a patient may perform, various physiological processes, such as the patient's respiration and/or heartbeat, necessarily introduce motion into the examination process over the time interval in question. Such motion (voluntary or otherwise) can lead to artifacts and/or other discrepancies in the resulting visualizations, which may reduce or limit the ability of a caregiver or other medical professional to isolate the locations or locations of interest in a patient where the radiopharmaceutical is aggregated.